I like the inclosed underbelly as it keeps things cleaner but that shouldn't be a deal breaker as you can always do that yourself. I'm not familier with a vinyl roof only rubber. While looking at a used rig the roof needs special attention in the inspection process. Look for cracks, dry-rot, pin holes..... 03 isn't very old but depending on how it was maintained and stored the roof may become an issue. I keep my rig covered but not everybody can and UV can take its toll on the roof.
You state that the 246 has more insulation and in my opinion more is better. Helps keep you more comfortable in both hot and cold.
However you decide to go about purchasing a rig, new or used, do your homework, and inspect the heck out of 'em. If you are handy and can do minor repairs (which most RV repairs are) you could be very happy with a used rig. I purchased a 5 year old rig as my 1st 5er and was very happy with it.
Keep us posted on your hunting and keep the questions coming.